There are many occasions in which a sheet of material is passed between a pair of abutting rolls. Generally, the rolls are disposed horizontally, with one roll directly above the other roll, and one of the rolls, generally the lower roll, is maintained in a stationary position. The upper roll is urged into abutment with the lower roll, but will deflect upwardly to permit sheet material to pass between the rolls. The rolls may be powered to facilitate transport of the material, or the rolls may be utilized to control movement of the material. In some processes for coating sheet material, the rolls are utilized as wringers to wring excess cleaning and coating material from the sheet.
In the production of coated sheet material, the cleaning and squeezing of the coatings or solutions on sheet material has a significant effect upon the quality of the final product. The sheet metal itself, prior to coating, has imperfections such as small indentations or protuberances. The protuberances on the metal sheet may cause the rolls of the squeegee or wringers to lose contact with the solutions immediately downstream of the protuberance resulting in an imperfection in the coating of the sheet metal. It is one of the objects of the present invention to provide a roll assembly with a pressure actuator which minimizes imperfections in coatings applied to elongated strips of sheet material.
The inventor has found that imperfections in the applied solutions on sheet metal can be greatly reduced by adjusting the pressure exerted between the wringer rolls to an optimum value and maintaining that pressure. It is known that the application and removal of the coating or solutions that remain on the sheet metal after passing the wringer depends upon the pressure exerted on the sheet produced by the rolls. Conventional equipment utilized to remove solutions from sheet metal at the present time employs pneumatic cylinders to force the rolls toward each other and to place pressure on the sheet metal as it passes through the wringer. The inventor believes that protuberances in the sheet metal and solutions being removed force the rolls of the wringer apart, and in conventional equipment utilizing pneumatic cylinders, the movement of one roll with respect to the other results in translation of the piston with the air cylinder and an increase in the pressure within the air cylinder.
The force exerted by the air cylinder immediately following the passage of a protuberance on the sheet metal or solutions being wrung by the wringers is believed to result in a region in which the solutions are not removed or is uneven. Further, it often requires a period of time following a protuberance or solution passing between the rolls for the air cylinder to reach stabilization, resulting in hunting by the air cylinder, and such hunting produces an uneven layer of coating on the sheet metal. It is thus an object of the present invention to provide a roll assembly suitable for use as a squeegee or wringer with an improved actuator for controlling the pressure between the rolls.
Efforts have been made in the past to provide an improved actuator for use with squeeze rolls or wringers for use in the treatment of cloth, and U.S. Pat. No. 2,758,466 entitled SQUEEZE ROLL by Harold H. Belcher discloses an actuator for this purpose. The actuator of Belcher is a modified form of pneumatic cylinder in which membranes are utilized for seals.
In the past there have been many mechanical breakdowns for coating production lines as a result of failure of the actuator mechanism used to apply pressure to the squeeze rolls. The squeeze rolls operate in approximately the same range at all times, causing the piston of a pneumatic cylinder to move slightly with respect to a fixed position, thereby concentrating wear on the rings of the piston. As a result, pneumatic cylinders tend to fail when used as actuators for a wringer, resulting in disruption of production. It is a further object of the present invention to provide an actuator mechanism which is capable of long use in a wringer assembly without mechanical failure.
In past constructions, compliance in the linkage between the air cylinder and the movable roll have been a source of imperfection in coated or treated sheet. Compliance in the linkage has resulted in hunting or excessive snap-back pressure following the passing of a protuberance or solution in the sheet material. It is an object of the present invention to eliminate as far as possible linkage between the actuator and movable roll to avoid such sources of imperfections in the product.